Because most philosophies that frown on reproduction don't survive.

Thursday, December 12, 2013

This is Your Dog On Selective Breeding

Posting has been thin lately because I've been working long hours on a series of projects at work, and MrsDarwin continues on bedrest while her mother has been ably running the house. My attempts at blogging lately have mostly been along the lines of "I started to read this article which would be good to blog about, if I can finish reading it some day and then write about it."

Here's something interesting, though: how one hundred years of inbreeding have exaggerated the physical characteristics of pure bred dogs. A blogger collected photos of dog breeds from the 1915 book Dogs of All Nations and compared them to pictures of modern purebred dogs.

The most extreme example is the Bull Terrier, which these days is a pretty exceedingly ugly dog, but apparently back in 1915 was not.

(Go check out the original article for a number of additional examples.)

Obviously selecting for certain traits and breeding exclusively within a set population can produce increasingly extreme results. This has me wondering what the appropriate approach would be if you were breeding for stasis rather than breeding for increasingly extreme characteristics. I imagine part of the solution is simply not always picking the most extreme representatives of the population to pass on their genes, but it seems like you'd also have to cycle through outside genes with occasional outbreeding as well.


Cminor said...

Saw this a few weeks ago and, having a bully cross, found the image comparisons tantalizing. Have some thoughts on the issue, but will save them for when I'm not using a device that throws me out while I'm throwing a slice of pizza in the microwave!

cminor said...

There, that's better.
I'm no expert, but as I understand it breeders who know their stuff try to alternate inbreeding and outbreeding (within a breed) by generation to maintain desired characteristics while reducing the incidence of bad genes. A lot depends on whether your purpose in breeding is to raise potential conformity prizewinners or to produce dogs for other purposes (good breeders value breed improvement.) I've been told, for example, that hunt clubs, which are more interested in having a good selection of hounds with health and stamina, will air-freight dogs cross-country to broaden the family tree.

Things that get in the way of correcting some of the craziness that goes on in the way of producing a certain "look" include purebreed clubs, which can be pretty intolerant of anything that threatens their standards, a small gene pool to start with, and sloppy breeding practices by folks who don't know what they're doing or are just out to make a quick buck. (Re that last one, ask any German Shepherd enthusiast--nothing ruins a breed like a surge in popularity.) Of course, if your purpose in breeding was to emphasize certain characteristics that were incompatible with good health to begin with--as is the case in a number of the examples in the essay--problems are going to happen. Olde Englysshe Bulldogges, which are bred to avoid many of the problems of the modern English variety (and are actually sturdy and handsome dogs with more of a "classic" look, if bulldogs are your thing) nonetheless may carry some lethal traits associated with brachycephaly--a friend of mine bred two litters (same mother, different fathers) and lost a couple of pups each time as a result.

Recessive characteristics (which is what many of those "extreme" ones are) are tough to maintain, which incentivizes inbreeding. We assume our (rescued, ancestry unknown) bully cross had a pure bully parent based on her size, build, temperament, and bat ears (characteristic of bulls, Bostons, and few other dogs in her size range) but there's not a vestige (thank goodness) left of that ridiculous melon-shaped skull. OTOH, we've lost a couple of dogs with varying degrees of GSD ancestry to diseases that are particularly linked to the GSD breed; some of that bad stuff can be very persistent even after a few generations of outbreeding.

At risk of going on too long, the slavish devotion of many purebred fanciers to "breed standard" is at the root of a lot of the trouble, and may be a factor in the increase of "extreme" characteristics. Some examples I've read or heard of:
--Refusal by the AKC to recognize a breed (Carolina Dogs, to be exact, which are a "new" breed, but actually kind of a throwback to the wild type) until the stud book was closed (thus limiting the gene pool to those dogs already in it and their descendants, even if new individuals with all characteristics of the breed turned up available for introduction.)
--Refusal to allow outbreeding with a related, similar breed to save a breed (Dalmatians) overrun with health problems.
--Refusal to issue papers to offspring of a field trial champion retriever because the dog was a few inches taller than the breed standard.
I've heard that DNA testing suggests that some breeds show evidence of past crossbreeding (whether intentional or inadvertent, who knows) which makes all this fussiness about as convincing as one of those Oscar Wilde characters who worries about being seen with the wrong people when his mother was of notoriously easy virtue. I understand the desirability of certain traits, but ruining animals' health to keep achieving them is insanity. Dog breeds have been going extinct since men started breeding dogs--some of these breeds need to be opened up to a little genetic variability, or just let go (I'm looking at you, Ugga.)

Darwin said...

Thanks, CMinor. As a non-dog person, I didn't know any of that and it's fascinating. I'm particularly interested reading around briefly on the Olde Englysshe Bulldogg and the idea of re-breeding to get a population like the population of a purebreed that used to exist 100-200 years ago.

Sarah said...

That's interesting. What's sad to me is not the relative "ugliness" of some super-selected breeds but the health problems that can result. For instance, the University of Georgia has a direct line of bulldogs for the mascot, but they all have terrible health due to inbreeding. Apparently purebred bull dogs have to born via Cesarian rather than naturally due to their large heads.